One type of device for allowing a person to descend by means of a rope is shown in U.S. patent application Ser. No. 296,374 filed Aug. 26, 1981, which corresponds to European Patent Application No. 81106095.3 (publication No. 0 046 891 A3, published Mar. 10, 1982). The embodiment of such a device, as illustrated in FIGS. 7 through 10 of this application, shows the rope first passing one and a half times around a friction cylinder and then passing over an additional friction body. In the process the rope is diverted by approximately 180.degree.. The rope then passes along a flat braking surface on the additional friction body past a pivoting cam control lever which is biased against the rope by a spring. The rope always exerts a certain friction on the cam control lever while sliding between the braking surface and the control lever. The rope tends to pivot the control lever so that it wedges the rope between the braking surface and itself to bring the device to a standstill on the rope, provided that the control lever can move freely and is not arrested by a person intending to slide down the rope so that braking does not take place.
A disadvantage of this foregoing device is, first of all, that a spring is necessary to ensure functioning of the device. This spring is a weak point since it requires a functional examination at regular intervals to make sure the spring is not broken or rusty, or that the spring does not fail to function for any other reason when the device is being used after a long layaway. Also, the ability of the entire device to function hinges upon the proper functioning of the spring.
The embodiment of FIGS. 1 through 7 of the aforementioned application avoids this disadvantage by allowing the additional friction body, around which the rope passes, to pivot eccentrically so that it pivots during circulation of the rope and wedges the rope between itself and a braking surface, thereby arresting further movement of the rope. However, this device of FIGS. 1 through 7 is cumbersome and expensive. This device is also prone to failure when used in a rough environment since, where descent by rope is desired, force must be transferred from a control lever via a gear to the additional friction body to counteract the braking force of the additional friction body. Contamination of these gears may jeopardize functionality, and a number of precisely machined parts with close tolerances is required.
Known devices which allow persons to descend by means of a rope are not optimally simple. In addition, all of the following requirements for operational safety are not satisfied in known devices:
(a) the device should be usable with ropes having different diameters, within limits; the device should especially tolerate a diameter change arising from an increase in the diameter of the rope as a result of water absorption; PA0 (b) mechanical parts prone to failure such as springs and gear wheels are to be avoided; PA0 (c) the control lever, including the eccentrically mounted area needed for braking, should be easily interchangeable so that the device can be used with different ropes or rope diameters having larger differences than mentioned in paragraph (a); PA0 (d) speed control should be precise; PA0 (e) braking should occur even when the rope is accidentally inserted incorrectly, for instance, when the rope runs past the control lever in a direction other than the desired direction; PA0 (f) braking should take place even when the person using the device reacts incorrectly (that is, when he or she pulls or pushes the control lever to brake instead of letting it go); and PA0 (g) the device should be operable in different ways, i.e., for descending on the rope and for operating with the device locked in place.